All I can find at autozone is the single battery system with the single alternator shown here.
http://www.autozone.com/autozone/rep...All%20Gasoline)

If you look at the diagram, there is a "battery junction box". This is the underhood fuse box, and if you notice, they have a large fuse in there for the regular battery. I would check and see if you have another large fuse in there for the aux battery. And also follow the aux battery wiring and look for any open fusible links.

If I get time, I have the factory manual for your model at home, and I will see if they have the aux battery diagrams.